The Norwalk and Norwalk-like human caliciviruses are major etiologic agents of epidemic nonbacterial gastroenteritis. However, knowledge of the molecular epidemiology of these noncultivatable viruses is limited. Our goal is to characterize viral genetic determinants that are responsible for the antigenic diversity and epidemiologic importance of these pathogens. Towards this goal, we accomplished the following this year: (i) sequence analysis of approximately 2,600 consecutive bases from the genome of the Hawaii virus, a prototype 27nm Norwalk-like virus that was identified in previous volunteer cross-challenge studies in our laboratory as serotypically distinct from the Norwalk virus; (ii) sequence analysis of a segment of the RNA-dependent RNA polymerase- encoding gene of two other Norwalk-like viruses obtained from elderly nursing home patients; and (iii) cloning of the gene encoding the capsid protein and production of baculovirus-expressed self-assembled virus-like particles (VLPs) from the Desert Shield virus (DS395), Toronto virus (TV24, formerly designated "minireovirus"), and Hawaii virus (HV). Furthermore, we have used these recombinant VLPs to develop diagnostic assays for the detection of these viruses and have initiated molecular epidemiologic studies. In addition, examination of the antigenic relationships among these viruses is in progress.